This and a companion project (HD001123) investigate auditory communication in primates. The overall goal of these studies is to provide a comprehensive understanding of primate auditory communication in terms of development, neural mechanisms, endocrine factors, and social context. Two species, the squirrel monkey and the common marmoset, have been the main subjects of study, with additional data collected from other species where appropriate. The present project studies primate communication from a bioacoustic and ethological perspective, focusing on the detailed acoustic structure of vocalizations produced in natural settings, and the relationship of structural differences to differences in age, gender, experience and response selectivity, as well as the broader factors of social context and genetic background. Prior work in this project has determined that there is considerable individual variation in the detailed acoustic structure of infant cries, which is stable over at least the first 3 months of life. The project is currently focusing on the analysis of vocal data collected from our colony over a number of years, to produce a comprehensive picture of vocal development in the context of brief periods of social separation. This is a unique project, as no prior longitudinal analyses of vocal development in a non-human primate colony exist. Data have been collected from 3 species of non-human primate. This year, vocalizations collected during brief separations of common marmoset (Callithrix jacchus) infants in their first week of life have been analyzed. Thirty-six infants from one cohort (the 'J'cohort) were analyzed. Thirty-two were born as twins (the usual pattern in marmosets), with four additional singletons. Ages at birth ranged from 22 to 34 grams. Recordings were made 1-2 days after birth (during which time shaved patches were made in the fur to provide individual identification). Infants were gently separated from a parent and placed on a soft pad in a small, perforated weighing box in a separate, quiet room. Infants typically began vocalizing immediately upon separation. Recordings were terminated after 5 minutes or less, and the infant returned to its parents. Vocalizations made in this context were of 6 acoustic sub-types. About half of the twins produced calling patterns very similar to those of their twin sibling. Recordings were repeated at one week of age, using similar methods. Calling patterns were fewer, and, as a consequence, twin siblings shared calling behavior in most cases. These results represent the first comprehensive description of the calling behavior of neonates in a non-human primate. A database being developed by a certified genealogist, Judith Newman, will provide ready access to the familial relationships of the members of the colony, which will facilitate comparisons of the vocal behavior of related individuals.